1. Field of the Invention
With the advent of hybrid DNA technology, production of mammalian proteins in microorganisms became a reality. For the first time, mammalian proteins could be synthesized in a unicellular microorganism by introduction of a gene encoding for the mammalian protein under the transcriptional and translational control of regulatory sequences recognized by the microorganism host. The introduction of these foreign constructions into a microorganism host resulted in competition between the regulatory signals of the construct and the regulatory signal endogenous to the host for the host systems involved with expression. The structural gene of interest is usually directed to a product which, is nonproductive and may be injurious to the host. Therefore, host cells which can turn off the foreign gene can effectively dominate modified host cells.
Substantial progress has been made in isolating sequences concerned with transcriptional and translational regulation for protein expression. But frequently flanking sequences, as well as distant sequences, may also affect the efficiency and regulation of the expression of the protein. Therefore, as one manipulates these various sequences, removing them from their native environment, and joining them to unnatural sequences, that is sequences other than the wild-type sequence, one can never be certain as to the result.
In order to enhance the economies of producing proteins in microorganisms, there have been substantial efforts directed to improving the efficiency of transcription and translation, maximizing the proportion of total protein directed to production of the desired product, enhancing the viability of the modified host, as well as improving the efficiency with which the modified host may be obtained.
2. Description of the Prior Art
Guarente et al., Proc. Natl. Acad. Sci. USA (1982) 79:7410-7414, describes a hybrid promoter region employing the GAL4 regulatory region. Guarente and Ptashne, ibid. (1981) 78:2199-2203, report the presence of two domains in a yeast promoter, with a region upstream from the TATA sequence providing an activation site. Kramer et al., ibid. (1984) 81:367-370, describe the regulated expression of a human interferon gene in yeast employing the yeast acid phosphatase promoter, where expression is induced by phosphate or a temperature shift. Tekamp-Olson et al., Cold Spring Harbor Meeting, Molecular Biology of Yeast, 1983, describe the absence of deleterious effects on yeast viability when employing "short" promoters, as distinct from the presence of such effects, when employing an extended promoter region or "long" promoters.